8 or 16 ohm?

[espenj2005]

I?m a beginner, as you understand and i have some questions:
If i have to choose between 2 drivers, one 8 and one 16 ohm, what would be the best to go for( is it any differense in sound etc)?
I?m planning to purchase a 8 ohm woofer, would this force me to use 8 ohm for the other(compression) driver?

I understand this is the res for the driver but the practical meaning of this i don?t understand.
Thanks for any help!
Espen

[espenj2005]

thanks Martin!
This is good to know.
But if i cross the drivers passive and calculate the values after the drivers load, would it then be the same if i use 16 ohm for the compressiondriver and 8 for the woofer?
Thanks
Espen

[bfish]

A speakers ohm rating is a measure of impedance, which varies, depending on frequency, capacitance, inductance, AND resistance in an AC circuit. Resistance is a much simpler component, which is simply the resistance of flow to DC current (what you measure with an ohmmeter=DCR). Choosing speakers of the correct impedance to properly complete your system depends on how you choose to divide the program material into the appropriate frequency bands (crossover):

A. Passive Crossover-The most common setup. Here, the crossover input impedance should match the amp output impedance, and (unless you build your own crossover), must match all the driver impedances, i.e., all 8 ohms, or all 16, etc. Most factory-made speaker systems have this already accounted for, but if you build a system from components, you have to ensure everything is compatable, including impedance, power handling, bandwidth, etc.

B. Active (electronic) crossover-more expensive, more complex, but unbeatable when done right. Requires an amp channel for each driver employed, and an electronic crossover to divvy up the signal BEFORE the amps. Here, you have more impedance options, as only each amp channel must match the impedance of the driver it powers, though should still be "paired" (i.e., both woofers could be 16 ohms, while both horns could be 8, assuming you have those options on your amps.

16 ohm drivers were the standard in the old days, 8 ohms are more common, and have been the 'standard' for years. 4 ohm components are available, mostly newer, and there's still a few 32 ohm antiques around. Just make sure to load the amp(s) with the correct value. Generally, the only signifigant reason to choose 16 over 8 is (a.) you've already got 16s, or (b.)when there'll be long runs of speaker cable involved (>100'). There are some exceptions, but far too detailed for today.

[espenj2005]

This made it clear for me.
Thanks man
Espen

[Hornluvr]

There is no difference in sound quality between
8 or 16 ohm drivers, 16 ohm drivers were used mainly to ease the load on the amps, early transistors used to be pretty vulnerable.
You got to use a crossover and these are specified either
for 8 or 16 ohm drivers, so for your 8 ohm woofer
you must find an 8 ohm compression driver.
Regards, Martin

[just me now]

so what would be the potential problems associated with running 16 Ohm 515Bs on a 8 ohm Altec crossover?

Did Altec have the same (simmilar) issue with nominal impedence that early Lansing/JBL had?

[bfish]

"so what would be the potential problems associated with running 16 Ohm 515Bs on a 8 ohm Altec crossover?"

Using a single 16 ohm driver on an 8 ohm XO branch (or vice-versa) would be kind of like trying to swap the wheels and tires between a VW and a HumVee.....neither would perform as designed, even though they might function...sort of. A PAIR of 16 ohm 515Bs, paralleled for 8 ohms on an 8 ohm XO branch would work.


"Did Altec have the same (simmilar) issue with nominal impedence that early Lansing/JBL had?"

I'm not that familiar with early Lansing or JBL products, so I'm not really sure what you mean. By "nominal impedance", I'm assuming you mean the variance of a driver's impedance as a function of the frequency applied. Ideally, a driver's impedance would maintain a constant value, regardless of the frequency applied, but unfortuneately, it doesn't work that way. A driver's nominal impedance is specified as the "average" value observed over the bulk of its' intended operating range, even though there are peaks and dips in that value, particularly at resonance. Driver design involves a constant effort to minimze such variances. By using components as they were designed to be used, those peaks and dips are predictable and minimal.

[just me now]

i have read that the ohm indication label on certain early jbl drivers does not necessarily mean squat....

that they were known to manufacture identical drivers adn merely changed the foical to indicate whatever ohm....

[bfish]

That sounds kind of like a vicious rumor to me, production control would have to be EXTREMELY sloppy for such practice to need to occur. While most all parameters of a given drivers' construction have an effect on its' final impedance plot during developement, the production of subsequent copies of the same model in different impedances is strictly a function of the voice coil. The winding of a 16 ohm coil is signifigantly different from that of an 8, and either one can be easily and accurately reproduced, even if hand-wound, once the design pattern is made.

[just me now]

check out post #5 regarding the LE85...

http://www.audioheritage.org/vbullet...eled+impedence

I submit that it is not a vicious rumor, i don't know how widespread the practice was (maybe just limited to LE85).....